Mitsubishi SVZ ducted air handler
sk
| Posted in Mechanicals on
Hello,
My neighbor is looking at installing a Mitsubishi ducted air handler (SVZ-KP30NA with SUZ-KA30NA2 outdoor unit). From what I’ve read here on the GBA website (Dana Dorsett), the air handler does not have a truly variable output, but rather outputs in steps down to a low capacity of 12,640 BTU. Is this a correct understanding? If the output is in steps, does anyone know the size of the graduations? Thank you!
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Most ducted min splits I've logged for power had pretty continuous power draws that matched heat load through the day. I've never seen any steps, if there were steps, they were small enough to not matter.
The important part of using these is getting it right sized. Larger units have much higher min modulation capacity and oversizing can cause the unit to cycle (thus lower efficiency) large part of the year.
SUZ-KA30NA2 is also a non-hyper heat unit, which climate zone are you looking to install this in?
Seattle Washington area, Climate Zone 4. Hyper Heat not necessary. The house is about 1400 SF, 3 bedroom. Possible they may go with a 24K BTU unit. I am focused on how this will perform in cool weather (Fall/Spring) with respect to cycling. The min BTU output is a fair amount higher (12,640 BTU) than the the low end on a wall mount 1 to 1 ductless unit. The 24K unit I believe goes down to just below 10K BTU. I think the air handler will be a better fit for them than a 2: 1 multi-split.
I originally suggested they go with a 1:1 ductless (at much less cost plus better efficiency) in the main living area and use space heater in the second space, but that was a no-go for them.
I've learned a lot on this site, including that multisplits and ducted air handlers don't have the same modulating characteristics than the standard 1:1 ductless units do. Apparently, when people like Dana Dorsett have looked into it, the manufacturer will acknowledge the difference, which may explain why the equipment specs don't say as much as they do on the 1:1 units. At least this is how I understand it.
Speaking as someone who has a non-hyperheat Mitsubishi heat pump in Seattle, I would tell them to spring for the hyperheat if they can make it make sense, and if it doesn't, I would recommend the heat strip backup for those couple of really cold weeks a year. We were under the impression that the heat strip would be easy to add later if we turned out to need it, and that turns out not to be so for our system as it's installed, with our particular configuration of ductwork and so on. (I posted a question about that the other day that you might want to look at.) I would like to stress that we are mostly quite happy with our system, and it has not been expensive to run, but putting one in with old ductwork is always a bit of a kludge. And of course there are always going to be cases where the old ductwork is close to the end of its life, or isn't appropriately sized, or both.
Thanks for your insight. We did look at the Hyper heat models, and they have worse HSPF and COP ratings than the non-Hyper heat. I don't know why that would be. The Hyper heat model specs says "inverter driven compressor," while the non-Hyper heat says "variable speed inverted driven compressor." I had expected the Hyper heat to have better efficiency than the non-Hyper heat. As for heat strips, they will be getting those. I told them to get their ducts sealed/insulated if not already.
I would go through the calculations in this article first before selecting equipment:
https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler
I highly doubt anything 1400sqft code min construction zone 4 needs a 2.5 ton heat pump.
I have a SVZ and SUZ combination and I think it’s correct to say the indoor blower isn’t variable speed - it’s got a low, medium and high setting. As far as I can tell, the outdoor unit is variable speed, but maybe it’s just stepping down in unnoticeable increments. The indoor unit I leave on low 24/7, so variable wouldn’t really matter to me.
Yes, you are right. I recall the literature said that the air handler has a few set speed settings. However, you are saying that it appears the BTU output is variable? How does your system perform (cycling) during cool (not cold) weather?
The btu output is variable for sure. I don’t notice it cycling but it must because the turn down ratio is only ~ 2.5:1. It keeps the setpoint consistently, which the old furnace never could.
We have a MXZ-8C48NAHZ outdoor unit with 2 indoor SVZ (SVZ-KP30NA on the 1st floor and SVZ-KP24NA on the 2nd floor). Both are controlled by a Thermostat Interface (PAC-444). In both heating and cooling the indoor unit seems to ramp up gradually (along with the outdoor unit). I've never had the sense that they're oversized or noticeably short cycle in the shoulder seasons. In times of low demand the fan is so quiet you can't really tell it's running.
We've got great de humidification supported by the thermostat calling for 'low fan' via the PAC444.